#include	"b64.h"

const int CHARS_PER_LINE = 72;

void base64_init_encodestate(base64_encodestate* state_in)
{
	state_in->step = step_A;
	state_in->result = 0;
	state_in->stepcount = 0;
}

char base64_encode_value(char value_in)
{
	static const char* encoding = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
	if (value_in > 63) return '=';
	return encoding[(int)value_in];
}

int base64_encode_block(const char* plaintext_in, int length_in, char* code_out, base64_encodestate* state_in)
{
	const char* plainchar = plaintext_in;
	const char* const plaintextend = plaintext_in + length_in;
	char* codechar = code_out;
	char result;
	char fragment;

	result = state_in->result;

	switch (state_in->step)
	{
		while (1)
		{
	case step_A:
		if (plainchar == plaintextend)
		{
			state_in->result = result;
			state_in->step = step_A;
			return codechar - code_out;
		}
		fragment = *plainchar++;
		result = (fragment & 0x0fc) >> 2;
		*codechar++ = base64_encode_value(result);
		result = (fragment & 0x003) << 4;
	case step_B:
		if (plainchar == plaintextend)
		{
			state_in->result = result;
			state_in->step = step_B;
			return codechar - code_out;
		}
		fragment = *plainchar++;
		result |= (fragment & 0x0f0) >> 4;
		*codechar++ = base64_encode_value(result);
		result = (fragment & 0x00f) << 2;
	case step_C:
		if (plainchar == plaintextend)
		{
			state_in->result = result;
			state_in->step = step_C;
			return codechar - code_out;
		}
		fragment = *plainchar++;
		result |= (fragment & 0x0c0) >> 6;
		*codechar++ = base64_encode_value(result);
		result = (fragment & 0x03f) >> 0;
		*codechar++ = base64_encode_value(result);

		++(state_in->stepcount);
		if (state_in->stepcount == CHARS_PER_LINE / 4)
		{
			*codechar++ = '\n';
			state_in->stepcount = 0;
		}
		}
	}
	/* control should not reach here */
	return codechar - code_out;
}

int base64_encode_blockend(char* code_out, base64_encodestate* state_in)
{
	char* codechar = code_out;

	switch (state_in->step)
	{
	case step_B:
		*codechar++ = base64_encode_value(state_in->result);
		*codechar++ = '=';
		*codechar++ = '=';
		break;
	case step_C:
		*codechar++ = base64_encode_value(state_in->result);
		*codechar++ = '=';
		break;
	case step_A:
		break;
	}
	*codechar++ = '\n';

	return codechar - code_out;
}

int base64_decode_value(char value_in)
{
	static const char decoding[] = { 62,-1,-1,-1,63,52,53,54,55,56,57,58,59,60,61,-1,-1,-1,-2,-1,-1,-1,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,-1,-1,-1,-1,-1,-1,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51 };
	static const char decoding_size = sizeof(decoding);
	value_in -= 43;
	if (value_in < 0 || value_in > decoding_size) return -1;
	return decoding[(int)value_in];
}

void base64_init_decodestate(base64_decodestate* state_in)
{
	state_in->step = step_a;
	state_in->plainchar = 0;
}

int base64_decode_block(const char* code_in, const int length_in, char* plaintext_out, base64_decodestate* state_in)
{
	const char* codechar = code_in;
	char* plainchar = plaintext_out;
	char fragment;

	*plainchar = state_in->plainchar;

	switch (state_in->step)
	{
		while (1)
		{
	case step_a:
		do {
			if (codechar == code_in + length_in)
			{
				state_in->step = step_a;
				state_in->plainchar = *plainchar;
				return plainchar - plaintext_out;
			}
			fragment = (char)base64_decode_value(*codechar++);
		} while (fragment < 0);
		*plainchar = (fragment & 0x03f) << 2;
	case step_b:
		do {
			if (codechar == code_in + length_in)
			{
				state_in->step = step_b;
				state_in->plainchar = *plainchar;
				return plainchar - plaintext_out;
			}
			fragment = (char)base64_decode_value(*codechar++);
		} while (fragment < 0);
		*plainchar++ |= (fragment & 0x030) >> 4;
		*plainchar = (fragment & 0x00f) << 4;
	case step_c:
		do {
			if (codechar == code_in + length_in)
			{
				state_in->step = step_c;
				state_in->plainchar = *plainchar;
				return plainchar - plaintext_out;
			}
			fragment = (char)base64_decode_value(*codechar++);
		} while (fragment < 0);
		*plainchar++ |= (fragment & 0x03c) >> 2;
		*plainchar = (fragment & 0x003) << 6;
	case step_d:
		do {
			if (codechar == code_in + length_in)
			{
				state_in->step = step_d;
				state_in->plainchar = *plainchar;
				return plainchar - plaintext_out;
			}
			fragment = (char)base64_decode_value(*codechar++);
		} while (fragment < 0);
		*plainchar++ |= (fragment & 0x03f);
		}
	}
	/* control should not reach here */
	return plainchar - plaintext_out;
}